The invention relates to an apparatus for measuring the volume rate of flow of flowing fluids by means of a rotameter inserted in the flowing path of the fluid, in which the rotameter comprises a rotameter tube with transparent walls, and a float of non-transparent material is located within the rotameter tube and the position of the float corresponds to the volume of the flowing fluid.
The need of measuring the volume of streaming gases or liquid often arises both in laboratory and industrial equipment together with the need of recording the measured values. Furthermore, the regulation of the volume of flowing fluids e.g. to keep the flowing rate on a constant level is often required.
The rotational flow meter, or in other words the rotameters are commonly used devices for measuring the volume of flowing gases and liquids. Their use and application is simple, convenient and inexpensive. Apart from several other preferable features a common drawback of rotameters lies in that they can be read out only visually. The sudden changes in flowing volumes resulting from the often changing pressure of the streaming fluid can be compensated only by manual intervention and no reliable instrumental possibility exists for recording the measured values. The instrumental reading of a rotameter is a difficult and still partly unsolved problem, since the position of the float of the rotameter is not stable but it oscillates with small amplitudes. The axial size of the float is greater, in general substantially greater than the distance between adjacent scale readings that define the resolution of the measurements, and this distance is hardly greater than the oscillational range of the float.
The problem of instrumental flow measurements will be more complex, if it is considered that the measurement of the exact position of the float can be required anywhere within the comparatively long measuring section of the rotameter tube.
There are already conventional measuring devices for flow measurements based on the use of rotameters. Such devices are designed in general integrally with the rotameter and they cannot be demounted. From this constructional design follows that such devices cannot be combined with or attached to already existing and operating rotameters. Such devices comprise typically a signal transducer that provides a measuring signal with limited accuracy from the position of the float, end position switches and in given cases outputs for recorder connections. In such conventional instruments the free movement of the float of the rotameter is generally limited by a mechanical assembly or by the effect of a magnetical or electrical field, and this significantly increases the measuring error of the rotameter. In such constructions the rotameter tube is fully encircled by an inductive winding or by an other assembly that impedes the visual reading of the rotameter.